1. Field of the Invention
This invention relates to an ink jet printer, and in particular, to an ink jet printer which makes a cap for suctioning ink (hereinafter also referred to as a cap simply) provided become closely attached to the nozzle surface of ink, and by making the pressure inside the cap reduced to suction ink from the nozzles, practices a restoration processing.
2. Description of the Related Art
If an ink jet printer is not used for a long period of time, water content vaporizes from its ink nozzles, which raises the viscosity of the ink in the nozzles, and clogging up of the nozzles occurs. If printing is done in such a state, because no ink is jetted from the nozzles clogging up, white streaky unevenness is generated in the output image, to degrade the output image.
In order to avoid such a condition, the nozzle surface is covered with a cap at the time of a maintenance operation, a negative pressure is generated by a suction means such as a pump, and ink is suctioned from each of the nozzles. By doing this, a foreign object or the like is suctioned, and the nozzles are restored to become in the optimum state. By the practice of such a maintenance operation, the quality of print is maintained.
As regards the sequence of the restoration processing at this time, a failure of jetting owing to the clogging up of the nozzles is restored through the processes of “suction” (The cap is made to be closely attached to the nozzle surface, and ink in the portions clogging up is suctioned by the pressure reduction inside the cap.), “wait” (If the inside of the cap with reduced air pressure is suddenly opened, air is suctioned from the nozzles; therefore, one should wait until the pressure becomes close to the atmospheric pressure to prevent this.), “leak” (By making the inside of the cap communicate with the atmosphere, no significant difference of pressure between the inside of the cap and the atmosphere is to be produced when the cap is detached.), “detachment” (The cap is detached from the nozzle surface.), and “wipe” (Surplus ink adhering to the nozzle surface is wiped off.). However, the nozzle surface is still in a state of being in contact with ink even immediately after the suction of ink, and in many cases, a large amount of ink adheres to the nozzle surface, also after the cap is detached from the nozzle surface to make the nozzles open.
Up to this time, it has been disclosed in the publication of the unexamined patent application H7-68766, a technology in which a porous ink absorbing body for absorbing ink is incorporated inside the cap, suction is carried out with the detachment speed of the cap from the ink jet head lowered, and the amount of ink adhering to the nozzle surface is reduced.
However, in this method, there is a problem that a long time is required for the detachment of the cap from the ink jet head, which makes long also the sequence time required for a maintenance operation.
Further, as regards the cap disclosed in the publication of the unexamined patent application H7-68766, because approximately all the part of the inside is occupied by the ink absorption body, a pressure loss is easy to be produced at the time of suction owing to the ink absorption body itself becoming a resistance to the suction.
With the above-mentioned points of problem taken into consideration, the inventors of this invention investigated about it to form the ink absorption body to be thin. However, in that case, at a position in the cap far from its suction opening, that is, at a position close to the end portion in the lengthwise direction of the cap, the suction force is not sufficiently effective. For that reason, bubbles are easy to remain, and it has been found that there is produced a new problem that, when the cap is detached from the ink jet head, ink with bubbles mixed is kept attached to the nozzle surface.
As the result, this brings about a phenomenon that ink containing bubbles existing close to the above-mentioned position far from the suction opening is suctioned from the nozzles owing to a capillary phenomenon and causes a failure of jetting to occur. Therefore, if this method is used in a suction process at a slow detachment speed in such an apparatus as described in the publication of the unexamined patent application H7-68766, it means that an insufficient maintenance operation requiring a long time is carried out, which causes the necessity of carrying out a maintenance operation again; therefore, this increases the amount of waste ink to result in useless consumption of ink.
Further, in recent years, for the purpose of making the speed of ink jet printers and the definition of the recorded image higher, there is a tendency to increase the number of nozzles of ink jet heads.
Therefore, it also results in the caps for suctioning ink becoming longer-sized. As the result, as described above, in the neighborhood of the nozzles located far from the suction opening, there is a higher possibility of bubbles remaining, and the possibility of a failure of jetting also becomes higher in accordance with it.